1. Field of the Invention
The present invention relates to a vertical alignment table mechanism and, more particularly, to a vertical alignment mechanism having an alignment table for holding an object to be exposed to light, such as a board for forming a printed wiring board, or an exposure mask, supported in vertical attitude.
2. Description of the Related Art
An etch-proof treatment of a conductive foil in a printed wiring board fabricating process exposes a precursory etching resist film to light through an exposure mask provided with an exposure pattern corresponding to a desired conductor pattern. The exposure mask and a board coated with the precursory etching resist film are aligned (registered) before exposing the precursory etching resist film to light. Generally, the board for a printed wiring board or the exposure mask is held by an alignment table capable of being moved for positional adjustment in a plane perpendicular to a direction in which the board and the exposure mask are arranged, and the alignment table is moved to align the board and the exposure mask with each other.
A variety of alignment table mechanisms for the alignment of the board and the exposure mask have been proposed. Basically, the alignment table mechanism is provided with an XYxcex8 table and achieves the alignment of the board and the exposure mask by moving the alignment table while errors in the superposition of register marks formed on the board and the exposure mask are measured by cameras or the like.
Referring to FIG. 5 showing a prevalently used conventional horizontal alignment table mechanism as an example, there are shown a horizontal base plate 3 and an alignment table 5 for holding an exposure mask or the like. The alignment table 5 has the shape of a rectangular flat plate and is provided with a relatively large opening 5a for allowing light to pass therethrough, surrounded by a peripheral portion thereof. The alignment table 5 is supported for free horizontal movement on attached to the upper surface of the base plate 3. First and second actuators 9 are attached to the front side of the base plate 3 with their axes extended rearward. A third actuator 9 is attached to the right side of the base plate 3 with its axis extended toward the left. The first, second and third actuators 9 are electric actuators provided with linearly moving operating rods 9a, respectively.
First and second guide rails 11 are attached to the front side of the alignment table 5, and a third guide rail 11 is attached to the right side of the alignment table 5. Sliders 13 are attached to the guide rails 11, respectively. Free end portions of the operating rods 9a are joined to the sliders 13 by universal joints 15, respectively. The third actuator 9 is driven to move the alignment table 5 rightward or leftward. The first and second actuators 9 are operated to move the alignment table forward or backward. Either the first or the second actuator 9 is operated to turn the alignment table 5 in a horizontal plane.
The overall size of the conventional alignment table mechanism 1 is large, for the size of the alignment table 5 because the actuators 9 project outward greatly from the periphery of the alignment table 5. If it is necessary for the actuators 9 to move the alignment table 5 to locate the alignment table 5 with accuracy on the order of micrometers, plays in the joints of the actuators 9 and the alignment table 5 including joining parts of the guide rails 11 and the sliders 13, and joining parts of the sliders 13 and the operating rods 9a, must infinitely be close to zero and, at the same time, the actuators 9 must be constructed in a precision that does not permit any backlash.
Although not shown in FIG. 5, actually, the actuator 9 is highly precision device including a pulse motor as a driving means, a ball screw, a coupling, and complicated precision bearings for supporting those components. Therefore, actuators 9 and the joints joining the actuators 9 to the alignment table 5 are expensive.
When an exposure implement, such as an exposure mask is used in vertical attitude with the intention of avoiding the adverse influence of dust, a vertical alignment table mechanism 1 as shown in FIG. 6 must be used. The vertical alignment table mechanism 1 needs a holding mechanism 17 to support the alignment table 5 between, for example, sliding bearings set in contact with the opposite major surfaces of the alignment table 5, respectively.
When the holding mechanism 17 is employed, the vertical alignment table mechanism 1 has a big depth and the external dimensions of the alignment table 5 must be increased for engagement with the holding mechanism 17. Consequently, the size of the vertical alignment table mechanism 1 increases. Generally, the alignment table 5 held by the holding mechanism 17 is unable to move smoothly and it is very difficult to eliminate backlashes in the holding mechanism 17. Part of the holding mechanism 17 projects on the front side of the alignment table 5, obstructs the movement of the alignment table 5 relative to an object with which the position of the alignment table 5 is to be adjusted, and places restrictions on the freedom of designing the alignment table mechanism 1 and the peripheral mechanisms.
The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide an inexpensive, compact vertical alignment table mechanism capable of achieving precision alignment.
According to the present invention, a vertical alignment table mechanism comprises: a vertical support wall; an alignment table disposed in a vertical attitude opposite to a front surface of the support wall, and having an exposure implement supporting region surrounded by a peripheral portion; a plurality of table support devices supporting the alignment table for movement in a vertical plane; and a plurality of table moving devices for moving the alignment table in directions parallel to two alignment directions perpendicular to each other; wherein each of the table support devices comprises an elastic member constantly biasing the alignment table toward the support wall, and a rolling member interposed between the support wall and the alignment table to allow the alignment table to move in the above directions.
In this alignment table mechanism, the alignment table is constantly pressed by an elastic members against the support wall through the rolling members so as to be movable. Therefore, there is no play at all in directions perpendicular to a vertical wall between the alignment table and the support wall.
Since the elastic members and the rolling members of the table support device do not project from the front surface of the alignment table on which the exposure implement is supported, the movement of the alignment table relative to an object with which the position of the alignment table is to be adjusted is not obstructed and hence the freedom of design of the alignment table mechanism and its associated mechanisms is increased greatly.
In this vertical alignment table mechanism according to the present invention, each of the table moving devices may comprise a pair of contact members attached to the support wall and the alignment table, respectively, so as to be in contact with each other, an elastic member for urging the contact members in contact with each other, and an actuator for moving one of the contact members toward and away from the other.
Thus, the alignment table does not have any play at all not only in the vertical plane but also with respect to alignment directions because the contact members are in pressed contact with each other at all times. Therefore, even if the actuator moves one of the contact members toward or away from the other in this state, the latter contact member follows the movement of the former to hold the alignment table with reliability, which insures a highly accurate alignment operation.
Since the elastic force urging the contact member on the side of the alignment table and the contact member on the side of the support wall in contact with each other serves as a preloading force acting on the operating rod of the actuator, the actuator need not be an expensive one incorporating complicated mechanisms for eliminating backlashes between its components and hence the manufacturing cost of the vertical alignment table mechanism is reduced accordingly.
In this vertical alignment table mechanism according to the present invention, the table support devices and the table moving devices may be disposed outside the exposure implement support region of the alignment table.
Since any portions of the table support devices and the table moving devices do not project to the outside or project scarcely to the outside from the alignment table, the vertical alignment table mechanism can be formed in a compact structure of dimensions corresponding to the necessary size of the alignment table; that is, the table support devices and the table moving devices do not require any large space for installation, the exposure implement support region, such as an opening, can be formed in a large size for the size of the alignment table.
The contact member driven for movement by the actuator may be attached to a free end part of the operating rod of the actuator or may be connected by an intermediate member to the free end part of the operating rod of the actuator. When the contact member is attached directly to the free end part of the operating rod, the table moving device can be formed in compact construction.
The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in connection with the accompanying drawings.